Efficacy of topical sunscreen preparations on the human skin: combined indoor-outdoor study.

The sun protection factors (SPF) of 35 commercially available sunscreen preparations were tested on human skin under various conditions. Five distinct groups of products, ranging from minimal (SPF 2 to less than 4) to ultra sun protection (SPF 15 to greater than 19) were evaluated. Claimed SPF values were not always consistent with those obtained in our tests. Substantivity studies of a randomly selected group of sunscreen preparations during the hot, highly humid Israeli summer showed mean SPF reductions of 47 and 60%, respectively, following exercise-induced sweating or a 20-min swim. Judicious selection and use of an appropriate sunscreen preparation according to individual skin type or life-style, as well as the introduction of strict testing and labeling regulations, are essential measures for reducing the risk of sun-induced skin cancer and malignant melanoma in Israel.